1. Field of the Invention
The invention relates to a semiconductor manufacturing process. More particularly, the invention relates to a method for forming a pattern in a substrate.
2. Description of Related Art
In general, a method for forming a pattern in a substrate includes forming a patterned mask layer on the substrate first. Thereafter, by using the patterned mask layer as a mask, an etching process is performed to form trenches in the substrate. Then, a material of the predetermined pattern is filled in the trenches.
With the tendency of device miniaturization and device integration, the sizes of the line width and the space of the devices are reduced. It is difficult to form the pattern having required line width and space by using the above method. Accordingly, a double patterning method is developed.
FIGS. 1A-1E are cross-sectional views showing a double patterning method in the related art. First, referring to FIG. 1A, a patterned photoresist layer 12 is formed on a substrate 10. The patterned photoresist layer 12 has a pattern which has a ratio of the line width to the space of 1:3. Then, referring to FIG. 1B, a spacer 14 is formed on the sidewall of the patterned photoresist layer 12. A thickness of the spacer 14 is equivalent to a line width of the patterned photoresist layer 12. Subsequently, referring to FIG. 1C, the patterned photoresist layer 12 is removed. Thereafter, referring to FIG. 1D, using the spacer 14 as a mask, an etching process is carried out to form trenches 16 in the substrate 10. After that, referring to FIG. 1E, a conductive material 18 is filled in the trenches 16. As such, a conductive pattern having a ratio of the line width to the space of 1:1 is formed in the substrate 10 (a top view thereof is shown in FIG. 2).
In the method, the patterned photoresist layer 12 has the pattern with a ratio of the line width to the space of 1:3 so that the patterned photoresist layer 12 can be easily formed if the device size is smaller and smaller and the conductive pattern having the ratio of the line width to the space of 1:1 is further liable to be formed.
In some specific requirements, the conductive pattern needs be modified. For example, one of the conductive layers in the conductive pattern may require to be cutted. In specific, for cutting one conductive layer depicted in FIG. 2 at where the rectangle 20 is, a mask layer 22 as depicted in FIG. 1B needs be formed at the location corresponding to the rectangle 20 before performing the etching process depicted in FIG. 1C such that the portion of the substrate 10 at the rectangle 20 is prevented from being formed with a trench 16. Accordingly, the conductive pattern with the cut pattern is formed after the conductive material 18 is filled in the trenches 16.
However, the fabrication of the mask layer 22 requires the use of an additional mask, which increases the fabrication cost. In addition, for achieving a smaller and smaller line width, the fabrication of the mask layer is quite difficult.